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'72 Hydrovac - brakes go to the floor

Unread postby broomeju on Fri Apr 20, 2018 7:14 pm

The brake system was working just fine until until i had engine trouble
I had someone work on the motor and now that's fine.

but, when we went to put the RV back on the road the brakes were locked-up
the shop replaced one of the Hydrovac booster units
that seemed to solve the braking problem
except..... the brakes now go to the floor once and on the 2nd "pump" I get a firm pedal

advice of the repair shop is that the brakes need to be adjusted
they feel that the pads are having to travel too far to make contact with the drums
of course the star wheels / adjusters are all bunged up so I'm looking at having to take them apart to fix the issue

the thing that does not make sense is that the pedal was high and firm before I had the engine troubles
it makes no sense that the brake pad clearances would change enough to require a full pump of the pedal to move the pads to the drum when before it only took a couple of inches of brake pedal movement to engage them

I have bled the brakes but am concerned if I'm doing it correctly or not.
I first cracked the input lines from the master cylinder to each hydrovac and bled them there (my son slowly depressing the pedal)
no air was evident
then i bled at each wheel - no air was evident

any advice on how to approach this would be much appreciated !

thanks
broomeju
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Re: '72 Hydrovac - brakes go to the floor

Unread postby raysimmons on Sat Apr 21, 2018 6:00 am

mine has a bleeder valve also io the hydro unit (just a single) down on the chassis. if your brakes are locking up try pulling the vacum line that comes off the intake manifold off and see if that frees up the brakes. I had a brake lock up problem and found that released them. put it back on and until it got hot it was all ok. ended being a bad hydro unit as I recall. (bad internal check valve ?)
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Re: '72 Hydrovac - brakes go to the floor

Unread postby broomeju on Sat Apr 21, 2018 6:32 pm

Thanks.

I tried a few things:

Manually bled --- old style with someone pressing the brake pedal slowly and cracking bleeder on down stroke closing at bottom, repeat, etc.

at the forward Hydrovac I was able to get a nice clean stream of brake fluid. zero air bubbles

at the rear Hydrovac I couldn't find a way to get the air out.
there is a bleed port right near to where the line from the master cylinder enters the Hydrovac
I even took a 15' vinyl tube and returned it to the master cylinder reservoir with the end of the tube positioned under the liquid level
even with more than 40 slow pumps of the brake pedal I could not get the air out!!!

I'm baffled.
The master cylinder reservoir is full up and the front line from the master cylinder has no air
but, the back feed to the Hydrovac is full of air and I can't get rid of it
any ideas?

I don't have any brake fluid leaks in the system anywhere that I can find.
When I start the engine and make two pumps of the pedal I then get a solid pedal and strong braking power and the pedal does not "sink" down

could that rear hydrovac be allowing air to enter into the brake fluid stream when the pedal is released and pressure is reversed on the system----like a seal is OK sealing under pressure but leaks air in under vacuum???

I also tried to use the power bleeder I have but my attempts to fashion an adapter/cover were close but never was able to get it to seal properly --- made a heck of a mess in the process

does anyone know of an adapter for the old style master cylinders
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Re: '72 Hydrovac - brakes go to the floor

Unread postby raysimmons on Sat Apr 21, 2018 7:49 pm

what about cracking a line open aft of the rear hydro ? let it gravity feed while keeping an eye on the fluid level if it won't bleed by pumping
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Re: '72 Hydrovac - brakes go to the floor

Unread postby broomeju on Sun May 06, 2018 12:30 am

:cry: Quick update and hope info. is useful to others.....

1) I tried and tried but could not bleed the master cylinder itself. I ran a hose from the Hydrovac bleed port all the way back to the master cylinder reservoir. Could not get rid of bubbles. So, I purchased UP 811 rebuild kit for NAPA and rebuilt the Wagner Tandem master cylinder . That worked out well. all parts fit. Used a Scotch Brite pad skewered on a threaded rod and held fast with washer and nuts(double nut on end) to clean up the bore.

2) purchased the motive adapter #1105. It sealed at the top of the master cylinder nicely. (It worked better with C-clamps than the chains provided). I have a garden sprayer converted to a power bleeder for other cars but this adapter worked great. I tried to make one but material wasn't thick enough and could not get it sealed so just broke down and purchase the right tool for the job.

3) with the master cylinder rebuilt then used the power bleeder to bleed the whole system and everything is "back to normal" . Very solid braking at this time.

4) also purchased some 1/2" hose and ran the vacuum line from the engine forward and up alongside the top engine coolant hose and then back to the hydrovac. According the super resource site http://dave78chieftain.com it is important to have the vacuum line go up 8-10" before it goes back to the Hydrovac to prevent gas or gas vapor from ruining the seals (see here: http://dave78chieftain.com/HydroVac_brakes.html)
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Re: '72 Hydrovac - brakes go to the floor

Unread postby broomeju on Mon May 14, 2018 11:42 am

broomeju wrote::cry: Quick update and hope info. is useful to others.....

1) I tried and tried but could not bleed the master cylinder itself. I ran a hose from the Hydrovac bleed port all the way back to the master cylinder reservoir. Could not get rid of bubbles. So, I purchased UP 811 rebuild kit for NAPA and rebuilt the Wagner Tandem master cylinder . That worked out well. all parts fit. Used a Scotch Brite pad skewered on a threaded rod and held fast with washer and nuts(double nut on end) to clean up the bore.

2) purchased the motive adapter #1105. It sealed at the top of the master cylinder nicely. (It worked better with C-clamps than the chains provided). I have a garden sprayer converted to a power bleeder for other cars but this adapter worked great. I tried to make one but material wasn't thick enough and could not get it sealed so just broke down and purchase the right tool for the job.

3) with the master cylinder rebuilt then used the power bleeder to bleed the whole system and everything is "back to normal" . Very solid braking at this time.

4) also purchased some 1/2" hose and ran the vacuum line from the engine forward and up alongside the top engine coolant hose and then back to the hydrovac. According the super resource site http://dave78chieftain.com it is important to have the vacuum line go up 8-10" before it goes back to the Hydrovac to prevent gas or gas vapor from ruining the seals (see here: http://dave78chieftain.com/HydroVac_brakes.html)


Also added 12mm which is about 1/2” check valve. Found valve on Amazon seller Lenmumu. It is fuel safe. Worked fine. About $25 total Between air brake hose and hose clamps from Napa and one-way valve seems no brainer to help prevent damage to Hydrovac units.
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Re: '72 Hydrovac - brakes go to the floor

Unread postby 67Travco on Fri Aug 10, 2018 6:19 pm

Hi - we are in the process of having to redo the brakes on our 67 travco - any assistance will be appreciated - the dave chieftain site is down and every foru references to it but nowhere did anyone post any of the info.

Thanks in advance - fyi we have P375 stamped on the plate - with 2 hydravac units and an MC under driver seat.
“The LORD makes firm the steps of the one who delights in him; though he may stumble, he will not fall, for the LORD upholds him with his hand.” Ps. 37:23-24
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Re: '72 Hydrovac - brakes go to the floor

Unread postby rjsdotorg on Wed Aug 15, 2018 7:00 pm

67Travco wrote:Hi - we are in the process of having to redo the brakes on our 67 travco - any assistance will be appreciated - the dave chieftain site is down and every foru references to it but nowhere did anyone post any of the info.

Thanks in advance - fyi we have P375 stamped on the plate - with 2 hydravac units and an MC under driver seat.


https://web.archive.org/web/20180411071 ... eftain.com

Also call Alretta Truck parts
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